Flame retardant hot melt compositions

ABSTRACT

The present invention relates to a flame retardant hot melt composition comprising from about 20% to about 60% by weight of the adhesive of at least one copolymer of ethylene, from about 10% to about 50% by weight of the adhesive of a flame retarding hydrated inorganic compound, from about 10% to about 30% by weight of at least one high melting point wax and from about 1% to about 10% by weight of at least one tackifying resin.

FIELD OF THE INVENTION

This invention relates to an ethylene copolymer based flame retardanthot melt adhesive composition.

BACKGROUND OF THE INVENTION

Hot melt compositions find use as adhesives, coatings and sealants.These compositions do not, however, have good flame retardingcharacteristics in and of themselves, making it necessary to add flameretarding compounds which function under heat to yield compositionswhich are more difficult to ignite. These compounds act under intenseheat and high temperatures by absorbing heat, by decomposing to form anonflammable ash or coating to provide a barrier against heat transferor by evolving products such as water vapor which retards or stopsfurther propagation of a fire. Flame retardancy is measured by theoxygen index which is a vertical burning test. An oxygen index of 21indicates that a composition would burn in atmosphere so the oxygenindex is generally required to be 23 or higher to have flame retardingcharacteristics. The smoke generation of these materials must also beacceptably low before they will be approved for use by the Underwriters'Laboratory (UL).

Both organic and inorganic compounds have been used for flameretardancy. Organic flame retardants include chlorinated paraffins,phosphate esters, chlorinated alicyclic hydrocarbons, fluoropolymers,polyvinyl chloride and a variety of other halogenated organic compounds.Halogenated compounds produce products having poor thermal stabilityresulting in poor color retention and production of noxious fumes. InU.S. Pat. No. 4,169,082 to Kusterer, Jr. issued Sep. 25, 1979, achlorinated paraffin wax is used as the flame retardant. Suchhalogenated compounds have been found to produce too much smoke in thecompositions of the present invention. The disadvantages of usinghalogenated compounds are described in U.S. Pat. No. 5,378,856 to Allenissued Jan. 3, 1995. Usually these compounds are used in conjunctionwith an inorganic flame retardant such as antimony oxide.

Inorganic compounds, also referred to as fillers, include antimonyoxide, magnesium hydroxide, zinc borate, barium metaborate, aluminatrihydrate, zinc oxide, ammonium octamolybdate and magnesium distearate.

Polymeric based hot melt compositions containing flame retardantmaterials have been used for many purposes including sealing andjacketing of power cables, insulation and jacketing of electricalconductors and coatings for electrical and optical wires wherein thepolymeric composition acts as a layer of insulation. The compositionstypically used in these areas have a polymeric material and a filler.These types of compositions may be found in U.S. Pat. No. 4,849,135 toReitz issued Jul. 18, 1989; U.S. Pat. No. 4,948,669 to Rolland issuedAug. 14, 1990; U.S. Pat. Nos. 4,575,184 and 5,059,651 to Ueno issuedMar. 11, 1986 and Oct. 22, 1991, consecutively; U.S. Pat. No. 5,378,856to Allen issued Jan. 3, 1995 and U.S. Pat. No. 5,482,990 to Jow et al.issued Jan. 9, 1996.

U.S. Pat. No. 5,059,651 to Ueno specifically teaches a flame retardantand smoke suppressed polymeric composition comprising a radiation curedcopolymer of ethylene and vinyl acetate containing 50-85% by weightvinyl acetate and a flame retarding and smoke suppressing amount of afiller mixture. These compositions contain uncrosslinked vinyl acetatepolymers which gain strength only upon curing. At column 3 lines 37 to43 it is stated that "a copolymer of ethylene and vinyl acetatecontaining about 60% by weight of vinyl acetate and having a molecularweight of about 200,000, as admixed with the same weight of a finelydivided inorganic filler (aluminum hydroxide), has a tensile strength aslow as 0.1 kg/mm², and is of no practical use." Furthermore, thesecompositions are very high in viscosity and are intended to be used assheathing for electrical wire.

U.S. Pat. No. 5,317,051 to Harashige et al. issued May 31, 1994 teachesa flame-retardant olefin polymer composition superior in surfacewhitening prevention having a blend of a resin component consistingprincipally of an olefin resin and an olefin polymer modified with anunsaturated carboxylic acid or derivative thereof, a flame retardant anda whitening preventing agent. Harashige teaches that these compositionsare useful for electric wires, cables, packages, sealing materials,hoses, films, molded products and master batches.

In addition to the above applications, flame retardant compositions areuseful in the air filter industry, and in particular are useful for HighEfficiency Particulate Air (HEPA) Filters. In this situation, thecompositions act as adhesives to adhere the pleats of the filterstogether. These adhesives are extruded onto the filters and each filterpleat is adhered to the next. The difficulty in using the polymericcompositions described above is that the viscosities of thesecompositions are too high for use in hot melt application equipment. Inorder to lower the viscosity of a hot melt adhesive, it is common toreplace part of the polymer with lower molecular weight materials suchas resin and wax. However, when commonly used proportions of thesematerials are used, the smoke generation upon burning is unacceptablyhigh. In addition, lowering the polymer content to decrease viscositycan result in decreased filler acceptability and decreased flexibilityof the resultant composition.

HEPA filters utilizing a hot melt adhesive as a filter pleating adhesiveare discussed in U.S. Pat. No. 4,365,980 to Culbert et al. issued Dec.28, 1982. Culbert discusses utilizing a hot melt adhesive, "InstantLok," supplied by National Adhesives, Inc. This hot melt is ethylenevinyl acetate based and is generally used for case and carton sealing.It has greater than 25% tackifying resin, has no flame retardant and istherefore not a flame retardant adhesive. See column 3 lines 63 to 68.

It is an object of the present invention to provide a novel polymericbased flame retardant composition which has a relatively low viscosity,is flexible in a thin bead or film and adheres well to a variety ofporous substrates while maintaining a high oxygen index and low smokegeneration.

SUMMARY OF THE INVENTION

The present invention relates to a flame retardant hot melt compositioncomprising from about 20% to about 60% by weight of the adhesive of atleast one copolymer of ethylene, from about 10% to about 50% by weightof the adhesive of a hydrated inorganic compound, from about 10% toabout 30% by weight of at least one high melting point wax and fromabout 1% to about 10% by weight of at least one tackifying resin.

The present invention further relates to a flame retardant hot meltcomposition consisting essentially of from about 20% to about 60% byweight of the adhesive of at least one copolymer of ethylene, from about10% to about 50% by weight of the adhesive of a hydrated inorganiccompound and from about 10% to about 30% by weight of at least one highmelting point wax.

The resultant composition is characterized as having an oxygen index ofgreater than about 23 and preferably greater than about 25 and a smokenumber preferably less than about 6, more preferably less than about 5and most preferably less than about 3.

The resultant composition is further characterized as having a viscosityof less than about 30,000 cPs at about 135° C., preferably less thanabout 25,000 cPs and most preferably less than about 20,000 cPs andYoung's Modulus from about 1500 kg/cm² to about 10,500 kg/cm² andpreferably from about 2500 kg/cm² to about 6000 kg/cm².

The compositions are useful where flame retardancy is a requirement,specifically in the air filter industry and in particular for HighEfficiency Particulate Air (HEPA) filters.

The present invention further relates to a High Efficiency ParticulateAir Filter comprising a material effective for filtering airbornecontaminants and an adhesive applied to the material wherein theadhesive comprises from about 20% to about 60% by weight of the adhesiveof at least one copolymer of ethylene, from about 10% to about 50% byweight of the adhesive of a hydrated inorganic flame retarding compoundand from about 10% to about 30% by weight of at least one high meltingpoint wax.

The filter may be pleated prior to or after application of the adhesiveto the filter media or filter material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The copolymers of ethylene useful to the present invention includeethylene n-butyl acrylates, ethylene methyl (meth) acrylates, ethyleneethylacrylates and interpolymers of ethylene with at least one C₃ to C₂₀α-olefin. Ethylene n-butyl acrylate copolymers are available from suchcompanies as Elf Atochem North America in Philadelphia, Pa. under thetradename of Lotryl®, from Exxon Chemical Co. in Houston, Tex. under thetradename of Escorene®, from Du Pont de Nemours & Co. in Wilmington,Del. under the tradename of Elvaloy® and from Millennium Petrochemicalsin Rolling Meadows, Ill. under the tradename of Enathene®. Ethylenemethyl acrylate copolymers are available from Exxon Chemical Co. underthe tradename of Optema®. Ethylene vinyl acetate copolymers areavailable from Du Pont under the tradename of Elvax® and from MillenniumPetrochemicals under the tradename of Ultrathene® to name only a couple.The term "copolymer" in the present sense is simply meant to refer tocopolymerization of ethylene and also encompasses the use ofterpolymers.

The interpolymers of ethylene with at least one C₃ to C₂₀ α-olefin arehomogeneous linear or substantially linear polymers furthercharacterized in that each interpolymer has a polydispersity of lessthan about 2.5. These polymers are available from Exxon Chemical Co.under the tradename of Exact®, which are ethylene-butene copolymers andunder the tradename of Exxpol® which are ethylene-propylene copolymers.Ethylene/1-Octene copolymers are available from Dow Chemical Co. inMidland, Mich. under the tradenames of Affinity®, Insite® and Engage®.

The polymers preferable for use in the present invention preferably havea melt index greater than about 400 g/10 minutes as measured by ASTM D1238 and more preferably greater than about 800 g/10 min. The testingconditions used are commonly 190° C. with a 2.16 kg weight. Testingconditions are generally specified by the manufacturers of the polymersand are determined by such things as the molecular weight and meltingpoint of the polymer. Commercially available ethylene copolymersgenerally have melt indices of no greater than about 5000 g/10 minutes.Ethylene copolymers having higher copolymer contents, such as greaterthan about 25% copolymer by weight, generally have melt indices of lessthan about 3000 g/10 minutes and more commonly less than about 2500 g/10min. The copolymer content is preferably from about 25% to about 45% byweight of the polymer and preferably from about 25% to about 35% byweight of the polymer. Increasing the amount of the copolymer to greaterthan about 45% by weight results in a polymer that is very soft, lackssufficient tensile strength and may remain tacky at room temperature. Itis surmised that the polarity of these compounds help to better disperseand retain the inorganic fillers. Having copolymer contents ranging fromabout 25% to about 45% by weight helps increase desired flexibility inthe final composition. In a preferred embodiment, an ethylene vinylacetate copolymer having a vinyl acetate content of about 28% by weightof the polymer and melt index of about 400 g/10 minutes is utilized. Inanother preferred embodiment, a blend of ethylene vinyl acetatecopolymers having a vinyl acetate content of about 28% and having meltindices of 800 and 2500 g/10 min. is used.

The current inventors envision that other polymers could be used incombination with the copolymers of the present invention provided thatthe desirable characteristics of the final hot melt composition are notaltered.

The flame or fire retardant compounds useful to the present inventioninclude hydrated inorganic compounds, or metal hydrates, which functionby absorbing heat, evolving water vapor or steam which dilutescombustible gases being generated, producing a nonflammable char barrierbetween the heat source and the material and also functions as a smokesuppressant. These compounds have the advantage that they do not containhalogens which are noxious and can be quite toxic when released.

Examples of useful flame retardants, also properly referred to asfillers, include alumina trihydrate, magnesium hydroxide, hydratedcalcium silicates, hydrated calcium carbonates and basic magnesiumcarbonates.

Sources of alumina trihydrate flame retardants include Akron ChemicalCo. in Akron, Ohio, Aluchem Inc. in Ohio, CSA Chemical in New Jersey,Fiberchem Inc. in Washington, GCA Chemical Corp. in Connecticut, GreatLakes Minerals Co., Specialty Products Division in Michigan, HarwickChemical Corp. in Ohio, R.J. Marshall Co. in Michigan, New EnglandResins & Pigments Corp. in Massachusetts, Smith Chemical & Color Co. inNew York, Summit Chemical Co. in Ohio and Westport Industries Inc. inMissouri. Sources of magnesium hydroxide (Mg(OH)₂) include the PolymerAdditives Group, a Division of R.J. Marshall Co. in Southfield, Mich.and J.M. Huber Corp. in Norcross, Ga. While the selection of a flameretardant filler is vast, the alumina trihydrate and the magnesiumhydroxide are preferably used in the present invention. Aluminatrihydrate, which has a greater degree of hydration, is most preferableto the present invention.

A zinc borate flame retardant filler may optionally be used in thepresent invention.

The zinc borate is known to act well as a smoke suppressant and isusually used in combination with antimony oxide for flame retardance inPVC, polyolefins, unsaturated polyesters, thermoplastic polyesters,epoxies, nylons, urethane and phenolics. See, for instance, U.S. Pat.No. 4,439,572 to Kindrick issued Mar. 27, 1984; U.S. Pat. No. 4,833,190to Cella et al. issued May 23, 1989; U.S. Pat. No. 4,921,897 to Danforthet al. issued May 1, 1990 and U.S. Pat. No. 5,298,544 to Goff issuedMar. 29, 1994. U.S. Pat. No. 5,059,651 to Ueno issued Oct. 22, 1991 useszinc borate in combination with hydroxides or carbonates of di- andtri-valent metals. These optional fillers are useful up to about 40% byweight of the composition, preferably from about 10% to about 20% andmost preferably from about 1% to about 10% by weight of the composition.The present inventors have found that while the zinc borate is useful toreducing smoke generation, it is not a necessary component. Alternativesto zinc borate may include barium borate, ammonium fluoroborate, bariummetaborate, zinc stearate, ammonium octamolybdate and zinc stannate tomention only a few.

One example of a zinc borate filler useful herein has the formula,2ZnO.3B₂ O₃.3.5H₂ O, or in other words, 45% ZnO, 34% B₂ O₃ and 20% waterhydration. The H₂ O content is between about 3.3 to 3.7 and the hydratedform is desired, although nonhydrated forms are available. The particlesize is usually 2-10 microns and the refractive index about 1.58. Thiscomposition may be found under the tradename of Firebrake® ZBmanufactured by U.S. Borax in Valencia, Calif. and marketed by Harwickin Akron, Ohio.

Any of these hydrated fillers can be surface treated with a saturated orunsaturated carboxylic acid having about 8 to about 24 carbon atoms andpreferably about 12 to about 18 carbon atoms or a metal salt thereof.Mixtures of these acids and/or salts can be used, if desired. Examplesof suitable carboxylic acids are oleic, stearic, palmitic, isostearicand lauric. Examples of metals which can be used to form the salts ofthese acids are zinc, aluminum, calcium, magnesium and barium. Examplesof the resultant salts include magnesium stearate, zinc oleate, calciumpalmitate, magnesium oleate and aluminum stearate. The amount of acid orsalt can be in the range of about 0.1 to about 5 parts of acid and/orsalt per one hundred parts of metal hydrate and is preferably about 0.25to about 3 parts per one hundred parts of metal hydrate. The surfacetreatment is described in U.S. Pat. No. 4,255,303. The acid or salt canbe merely added to the composition in like amounts rather than using thesurface treatment procedure. The surface treatment, while allowing thecompounds to more readily mix and disperse with polymers, is notnecessary and generally adds more cost to the resultant filler,therefore making it more undesirable where cost is an issue.

The waxes useful herein are those classified as high melting pointwaxes. These waxes typically having melting points greater than about80° C. and preferably greater than about 90° C. The waxes generallyhaving melting points no higher than about 120° C. and more typicallyare less than about 115° C. Useful waxes include synthetic high meltingpoint waxes and high melting point microcrystalline waxes. Synthetichigh melting point waxes include high density, low molecular weightpolyethylene waxes, by-product polyethylene waxes and Fischer-Tropschwaxes. By-product polyethylene simply refers to the fact that theproduct is a by-product of a process which is used to obtain anotherchemical. For instance, waxes may be produced as a by-product ofpetroleum cracking process. These by-product waxes are also highdensity, low molecular weight polyethylene. Preferred waxes includePetrolite® C-4040, Polywax® 1000, 2000 and 3000, low molecular weightpolyethylene waxes available from Petrolite Corp.; Escomer® H-101, amodified polyethylene wax available from Exxon Chemical Co. in Houston,Tex; Marcus® 100, 200 and 300, low molecular weight polyethylene waxesavailable from Marcus Chemical Co., a Division of H.R.D. Corp. locatedin Houston, Tex; and Paraflint® H-1, H-4, and H-8, Fischer-Tropsch waxesavailable from Sasol-SA/Moore & Munger in Shelton, Conn.

The microcrystalline waxes useful herein are those having about 50% byweight or more cyclo or branched alkanes with a length of between about30 and 100 carbons. They are generally less crystalline than the highmelting point polyethylene waxes, and have melt points of greater thanabout 80° C. Examples of these waxes include Be Square® 175 Amber Wax,an 80° C. melt point microcrystalline wax, Be Square® 185 Amber Wax, an85° C. melt point microcrystalline wax, and Be Square® 195 Amber Wax, a90° C. melt point wax all available from Petrolite Corp. and Petrowax®9508 Light, a 90° C. melt point wax available from Petrowax Pa., Inc.located in New York, N.Y.

In preferred embodiments, synthetic high melting point waxes are used.Although the microcrystalline waxes are also very useful, the viscosityof the finished product is generally higher with the microcrystallinewaxes.

These high melting point waxes are useful from about 5% to about 30% byweight of the composition and preferably from about 10% to about 30% andmore preferably from about 15% to about 25% by weight of thecomposition.

Other waxes may be used in combination with the high melting pointwaxes. These include paraffin waxes and lower melting pointmicrocrystalline waxes. The paraffin waxes useful herein are thosehaving a Ring and Ball softening point of about 50° C. to about 80° C.Useful examples include Okerin® 236TP available from Astor WaxCorporation located in Doraville, Ga., Penreco® 4913 available fromPennzoil Products Co. in Houston, Tex., R-7152 Paraffin Wax availablefrom Moore & Munger in Shelton, Conn., and Paraffin Wax 1297 availablefrom International Waxes, Ltd in Ontario, Canada. Examples of usefulmicrocrystalline waxes include Victory® Amber Wax, a 70° C. melt pointwax available from Petrolite Corp. located in Tulsa, Okla.; Bareco®ES-796 Amber Wax, a 70° C. melt point wax available from Bareco inChicago, Ill. and Okerin® 177, an 80° C. melt point wax available fromAstor Wax Corp. These waxes are useful up to about 20% by weight of thecomposition and preferably up to about 10% by weight of the composition.

A wax is necessary to the present invention to lower the viscositywithout increasing smoke generation. It has been found that utilizinghigh amounts of tackifying resins to reduce viscosity tends to alsoincrease the smoke generation. The high melting point waxes arepreferred to improve heat resistance as measured by peel and shearvalues.

Chlorinated waxes have been used as flame retardants such as in U.S.Pat. No. 4,948,669 to Rolland issued Aug. 14, 1990. However, thesecompounds have been found to produce too much smoke when used in thecompositions of the present invention. It has also been desirable tousers of flame retardants to eliminate the use of halogenated compoundsdue to the health and safety hazards of using such compounds.

The tackifying resins useful herein include aliphatic, cycloaliphaticand aromatic hydrocarbon resins and modified hydrocarbons; terpenes andmodified terpenes; rosins and modified rosins, including rosin esters,and mixtures thereof. One skilled in the art would know that theseresins are all available with different levels of saturation orhydrogenation. This is often measured by the bromine number. Forinstance, the Eastotac® series of cycloaliphatic hydrocarbon resins fromEastman Chemical Co. in Kingsport, Tenn. are available in the E, R, Land W grades. The E series typically has a bromine number of about 15,while the R, L and W series have bromine numbers of about 5. Theseresins are also available with different softening points of 100° C.,115° C. and 130° C. Eastotac® H-142R is also available with a brominenumber of about 5 and a softening point of about 140° C. Other usefulresins include Escorez® 5300 and Escorez® 5400, partially hydrogenatedcycloaliphatic petroleum hydrocarbon resins, and Escorez® 5600, apartially hydrogenated aromatic modified petroleum hydrocarbon resin allhaving softening points of about 100° C. and available from ExxonChemical Company in Houston, Tex.; Wingtack® Extra which is analiphatic, aromatic petroleum hydrocarbon resin, Wingtack® 86, anaromatic modified synthetic polyterpene hydrocarbon resin and Wingtack®95, a synthetic polyterpene all having softening points of less thanabout 100° C. and available from Goodyear Tire and Rubber Co. in Akron,Ohio and Arkon® P-70, P-90 and P- 100, synthetic petroleum hydrocarbonresins having softening points of 70° C., 90° C. and 100° C.consecutively and available from Arakawa Chemical (U.S.A.) Inc. inChicago, Ill. Further examples include Hercolite® 2100 which is apartially hydrogenated cycloaliphatic petroleum hydrocarbon resinavailable from Hercules, Inc. in Wilmington, Del. and Zonatac® 105 Litewhich is a styrenated terpene hydrocarbon resin, made from d-limoneneand available from Arizona Chemical in Panama City, Fla. Useful modifiedrosins include Sylvatac® 1103 and Zonester® 100 available from ArizonaChemical and Permalyn 305 available from Hercules which are allpentaerythritol rosin esters. All of these resins also have softeningpoints of less than about 100° C. Sylvatac® 1085, an 85° C. softeningpoint glycerol rosin ester of tall oil is another example of a usefulrosin based tackifier. It should be noted that there are numerous typesof rosins and modified rosins with differing levels of hydrogenationincluding gum rosins, wood rosins, tall-oil rosins, distilled rosins,dimerized rosins and polymerized rosins. Some specific modified rosinsinclude glycerol and pentaerythritol esters of wood rosins and tall-oilrosins.

Examples of useful pure alphamethyl styrene resins are Kristalex® 3070(70° C. softening point), 3085 (85° C. softening point) and 3100 (100°C. softening point) available from Hercules in Wilmington, Del.

It has been found that a small amount of tackifying resin helps to lowerthe viscosity, to improve adhesion characteristics and to improveflexibility as measured by Young's Modulus. The lower the Young'sModulus, the more flexible the adhesive. Too much resin results inunacceptable smoke generation. The tackifying resins are useful from 0%to about 10% by weight of the composition, preferably from about 1% toabout 10%, more preferably from about 3% to about 7% and most preferablyfrom about 3% to about 5% by weight of the composition.

The tackifying resins found to be preferable to the present inventionare those resins which are low in aromatic content and high insaturation, or in other words, are highly hydrogenated having few doublebonds. Preferably, these resins are hydrocarbon resin. Some preferredresins include the Eastotac® series of hydrocarbon resins and Escorez®5300 and 5400 which are hydrogenated cycloaliphatic hydrocarbon resins.It is surmised that these types of resins produce less smoke generationthan other types of tackifying resins. In a preferred embodiment of thepresent invention, 3% by weight of a hydrocarbon tackifying resin isused.

A liquid component or plasticizer may optionally be used in thecompositions of the present invention. The most relevant plasticizersare liquid elastomers including polybutenes and polyisobutylenes. Theseliquid components reduce viscosity and increase flexibility. Examples ofuseful plasticizers include Parapol® 1300, a liquid polybutene availablefrom Exxon Chemical Co. in Houston, Tex. and Indopol® H-50, H-100 andH-300, liquid butene homopolymers available from Amoco Corp. in Chicago,Ill. It is desirable that these liquid components do not increase thetack of the finished composition. They are useful in amounts up to about10% by weight of the composition.

A stabilizer or antioxidant is also preferably used in hot meltadhesives. These compounds are added to protect the adhesive fromdegradation caused by reaction with oxygen induced by such things asheat, light or residual catalyst from the raw materials such as thetackifying resin. Such antioxidants are commercially available fromCiba-Geigy in Hawthorne, N.Y. and include Irganox® 565, 1010 and 1076which are hindered phenols. These are primary antioxidants which act asradical scavengers and may be used alone or in combination with otherantioxidants such as phosphite antioxidants like Irgafos® 168 availablefrom Ciba-Geigy. Phosphite antioxidants are considered to be secondaryantioxidants and are generally not used alone. These are primarily usedas peroxide decomposers. Other available antioxidants are Cyanox® LTDPavailable from Cytec Industries in Stamford, Conn., and Ethanox® 1330available from Albemarle Corp. in Baton Rouge, La. Many suchantioxidants are available either to be used alone or in combinationwith other such antioxidants. These compounds are added to the hot meltsin small amounts and have no effect on other physical properties.

Other compounds that could be added that also do not affect physicalproperties are pigments which add color, fluorescing agents, UVabsorbers and odor masks. Of particular importance to the adhesives ofthe present invention are pigments including titanium dioxide which addswhiteness to a product. This can be important to the aesthetics of afinished article. Additives like these are generally added in smallamounts of less than 5% by weight of the composition, more typicallyeven less than about 2% by weight of the composition and are known tothose skilled in the art.

These compositions are characterized as having an oxygen index ofgreater than about 23 and preferably greater than about 25 (atmosphereis 21 and is unacceptable for flame retardance) as measured by TestMethod No. 1 for Oxygen Index included in this specification.

They are further characterized as having a smoke number of preferablyless than about 6 as measured by Test Method No. 2 included in thisspecification, more preferably less than about 5 and most preferablyless than about 3. It should be noted that this is a qualitative andsubjective test which may vary from operator to operator. It is also arelative rating of the examples tested.

They are further characterized as being flexible having a Young'sModulus, as measured by the Tensile and Elongation test found in theExamples Section of the Specification, from about 1500 kg/cm² to about10,500 kg/cm² and preferably from about 2500 kg/cm² to about 6000kg/cm².

The compositions of the present invention are light in color having ayellowness index (also b value or yellow-blue index) of less than 5 andpreferably from about 1 to about 3 as measured using a MinoltaChromameter, Model No. CR-331 and an L value or black-white index,another important indicator of whiteness of less than 100, preferablyfrom about 75 to about 100 and most preferably from about 90 to about100.

The viscosities are preferably less than about 30,000 cPs at about 150°C., preferably less than about 25,000 cPs and more preferably less thanabout 20,000 cPs at 150° C., although the acceptable viscosity willdepend on the temperature of application and the equipment used to applythe composition. The temperature of application of a compositioncontaining alumina trihydrate is typically about 135° C. to about 150°C., but may even be 120° C. or less but is generally never higher thanabout 150° C. because the aluminum trihydrate can begin to release waterof hydration at such temperatures. The temperature of application formagnesium hydroxide may be higher. The application temperature istherefore dependent on temperature at which the flame retardant isactivated. The viscosity is limited by the application equipment.

The peel values are greater than about 40° C., preferably greater thanabout 45° C., more preferably greater than about 50° C. and mostpreferably greater than about 55° C. Peel values are an indication ofthe heat resistance that a hot melt adhesive may have, or in otherwords, may be a measure of the temperature at which an adhesive bond mayfail. This is important for shipping and storage when the products maybe exposed to higher ambient temperatures. It is important to note thatthis is not an absolute number, but rather gives an indication, relativeto other hot melt adhesives, as to which hot melts have better heatresistance than others.

These compositions are useful in applications where flame retardingcharacteristics are desired and may be used in the filter industry, forpipe wrapping, as flexible heat duct sealants and for potting andencapsulation of electrical components. Of course, the physicalrequirements for the compositions will be different depending on theapplication in which they are used.

These compositions are particularly useful as adhesives for air filtersgenerally and specifically they are very useful for High EfficiencyParticulate Air (HEPA) filters. These filters remove airbornecontaminants and are used in highly technical manufacturing such as inthe medical, chemical, food processing, space, nuclear, semiconductorand computer industries.

HEPA filters are generally pleated to increase filter surface area. Thismay be accomplished by folding a continuous strip of material back andforth resulting in an accordion-like shape. It is necessary to keep thepleats of the filter separated or spaced apart in a permanent and securemanner for however long the filter may be used which may be accomplishedwith various types of spacers including adhesives.

The adhesive is generally applied to the material of the filter materialor filter media when the filter material is still in a continuous stripand has not yet been folded or pleated, or in other words, prior tofolding or pleating the filter material into the accordion-like shape.However, the adhesive may also be applied after pleating. The filtermaterial may also be referred to as the filter media, and for filtersrequiring flame retardancy, is generally made of a fiber glass compositematerial.

The adhesive may be applied in a continuous bead or it may be in adiscontinuous (intermittent or interrupted) or stitch pattern. In theformer case, the filter is pleated after the adhesive is applied butwhile the adhesive has not yet set and is still warm and ductile. In thelatter case, the adhesive is laid down in a pattern such that theadhesive is between the pleats and invisible when looking at the outsideof the filter. These filters have a honeycomb type appearance when theyare in the final form.

These filters come with differing numbers of pleats and the pleats mayhave different depths from filter to filter depending on air flowrequirements and the performance required of a particular filter. Theprocess of using the adhesive to bond the pleats, therefore supportingand separating them, is also referred to as pleat separation or filterpleating. Different types of HEPA filters are discussed in U.S. Pat. No.4,365,980 to Culbert et al. issued Dec. 28, 1982, U.S. Pat. No.4,885,015 to Goulet et al. issued Dec. 5, 1989 and in U.S. Pat. No.5,098,767 to Linnerston issued Mar. 24, 1992.

The filters are required to pass an Underwriters' Laboratory test, UL900 TEST PERFORMANCE OF AIR FILTER UNITS. There are two classes of airfilters: Class 1 and Class 2. A Class 1 air filter unit shall notproduce flame or sparks when subjected to the flame-exposure andspot-flame tests, and during the flame-exposure test shall not cause thedevelopment of an area of more than 16.1 cm² as measured below the smokedensity time curve.

Class 2 air filter units shall not produce flame or extensive (25 ormore) sparks which are sustained beyond the discharge end of the testduct when subjected to the flame-exposure test and shall not cause thedevelopment of an area of more than 58 cm² as measured below thesmoke-density time curve.

An adhesive material used for coating the filtering medium or other partof an air filter unit shall have a flash point of not less than 163° C.as determined by the Test Method for Flash and Fire Points by ClevelandOpen Cup, ASTM D92-78.

These test methods are available from UL (UL 900).

It is desired that the compositions of the present invention pass Class2 air filter unit testing. It is also possible to use the compositionson Class 1 air filters if the amount of adhesive used is decreased.

The following non-limiting examples further illustrate the invention.

Examples 1-8 and Comparative Example A

The adhesives were prepared using a high shear sigma blade mixer such asthose manufactured by J.H. Day in Cincinnati, Ohio. The temperature ofthese mixers is maintained between about 135° C. and about 150° C. Theethylene copolymers are first added to the mixer followed by the flameretardant fillers. The resultant blend is mixed until smooth andhomogeneous. The resin, wax and any liquid component are then slowlyadded to the mixture to prevent phase separation. Any antioxidant usedmay be added at any point during preparation including at the beginning,or split and added at different stages during mixing. The pigment may beadded at the end or also at any other point if one so chooses. Thisprocess may be altered depending on the choice and amounts of theingredients used of which one of skill in the art would understand.

Test Methods

1 . Oxygen Index

This test conforms with ASTM D 2863-74 Test for Flammability of PlasticsUsing the Oxygen Index Method (type D materials). The procedure is usedto determine the relative flammability of cast films of coatings,adhesives and sealants using the G.E. Oxygen Index apparatus formeasuring the minimum concentration of oxygen in a flowing mixture ofoxygen and nitrogen that will just support flaming combustion.

2. Smoke Generation (Smoke Number)

The Smoke Number is obtained using the same Oxygen Index apparatus as inTest Method 1 above. A 30-40 mil film was burned in a 30% oxygenenvironment for 1.5 minutes. The smoke generated is then visuallyobserved and was rated on a basis relative to other samples tested. Thesamples were then ranked on a scale of 0-10 with 0 being no smokegeneration and 10 being dense smoke. This is a qualitative andsubjective test and it should be understood that this may vary slightlyfrom user to user. The present inventors have rated the examples on arelative scale.

3. Melt Viscosity

The melt viscosities of the hot melt adhesives were determined on aBrookfield Thermosel Viscometer Model RVDVII+using a number 29BS (solidshaft) spindle. The speed is generally about 50 rpms but the speed, aswell as the spindle size, may be varied depending on the viscosity.

4. Color

A Minolta Chromameter CR-331 (Colorimeter) was used to measure color. Asample of adhesive was heated in an oven until just molten and is thenpoured onto release paper making sure that the sample, once cool andset, has no air bubbles. Three values are measured by the instrument: Lis the value obtained for lightness, a is the red-green index and b isthe yellow-blue index. The L value ranges from 0 (black) to 100 (white),a ranges from +red to -green and b ranges from +yellow to -blue. In thiscase, the L value and the b value are of importance in determining thewhiteness of the sample. For the b value, the more negative the whiterthe product or the more positive the yellower the product.

5. Tensile and Elongation, Young's Modulus

Young's Modulus was determined using ASTM D-638. The die used is an ASTMD-638 Type IV die. A one inch gauge with a video extensometer is used tomonitor elongation. The strain rate used is 5.08 cm/minute. Young'sModulus is a method of ranking the relative flexibility of adhesivefilms. The film thickness used is 20-30 mils. The resistance to tensiledeformation is measured at small strains. All samples were tested atabout 23° C. (room temperature).

6. Programmed Oven Peels

Peel and/or shear values were determined by placing samples in aprogrammed oven with 100 g weights for the peel mode and 500 g weightsfor the shear mode, and ramping the temperature up from about 25° C. to125° C. at 25° C./hour. The oven automatically recorded the temperatureat which the samples failed. Each sample was coated onto kraft paper byhand using glass rods or shims. A top sheet of kraft paper is rolleddown onto the bottom sheet of kraft paper onto which the hot melt ispoured. The rods are then used to roll the adhesive down as well as formating the top sheet of kraft to the bottom sheet. Release paper is usedon either side of a 2.54 cm strip on the bottom sheet of kraft paper.The resultant coating is then a one inch wide band that is about 8-10mils or about 0.02 cm to about 0.03 cm thick. Four to five bonds weremade for the peel mode and four to five bonds were made for the shearmode and the results were averaged.

                                      TABLE I    __________________________________________________________________________    Examples      1    2    3    4    5    6    7    8    9    A    __________________________________________________________________________    EVA (28-400)  --   --   --   --   --   --   --   --   --   25.5    EVA (28-800)  33.5 33.5 20.5 20.5 20.5 30   20   20   33.5 --    EVA (28-2500) --   --   15   15   15   30   --   15   --   --    Parapol ® 1300 polybutene                  --   --   --   --   3    --   --   --   --   --    Escorez ® 2596 hydrocarbon                  --   --   --   --   --   --   --   --   --   26.5    resin    Escorez ® 5400 hydrocarbon                  --   7    3    3    --   --   10   --   --   --    resin    Paraflint ® H-4                  20   13   15   15   15   10   25   15   --   9    synthetic HMP wax    Microcrystalline Wax 195° F.                  --   --   --   --   --   --   --   --   20   20.0    Alumina Trihydrate                  --   --   --   --   --   --   --   --   --   37.5    8 microns    Alumina Trihydrate                  --   --   --   --   35   --   --   --   --   --    6 microns    Alumina Trihydrate                  25   25   25   35   --   28.5 43.5 10   25   --    5 microns    Alumina Trihydrate                  --   --   10   10   --   --   --   --   --   --    4 microns    Firebrake ZB zinc borate                  20   20   10   --   10   --   --   38.5 20   --    Titanium Dioxide white pigment                  1    1    1    1    1    1    1    1    1    1    Viscosity @ 135° C.                  11920                       16520                            12320                                 12100                                      10900                                           18240                                                2220 13340                                                          19600                                                               9540    Viscosity @ 149° C.                  8300 11380                            8280 8500 7480 12420                                                1550 9320 13480                                                               --    Oxygen Index  25.5 24.5 25.5 26.5 25.0 23.5 27.0 24.5 25.5 25.5    Smoke Number  2    6    2    3    3    5    6    2    2    8    Young's Modulus                  8230 3060 5520 4695 4065 1960 10210                                                     5685 3910 3460    Color (L value)                  93.81                       94.70                            93.61                                 93.63                                      93.92                                           95.39                                                94.26                                                     95.70                                                          95.14                                                               92.98    Color (B value)                  1.60 1.85 3.00 3.10 2.45 2.60 3.10 1.15 3.45 4.75    __________________________________________________________________________

Example 1 illustrates a composition which is mid-range for allingredients and having no tackifying resin.

Example 2 illustrates a composition which has a relatively highertackifying resin content than the other examples tested. The smokegeneration is increased and is higher than what is preferable to thepresent invention but is still acceptable.

Example 3 illustrates a medium range composition for ingredients but hasless tackifying resin than Example 2 and also has less smoke generation.

Example 4 has the same ingredients as Example 3 but has only a hydratedinorganic flame retardant. A higher oxygen index and a slightly highersmoke number were obtained.

Example 5 illustrates a composition using a maximum amount of flameretardant and no tackifying resin. The flame retardant characteristicsare not improved in this instance. The Parapol® 1300 liquid polybuteneis used to improve flexibility in this case.

Example 6 illustrates the maximum amount of ethylene vinyl acetate whichmay be employed while still retaining an acceptable viscosity profilefor the finished product, and also represents a sample having a minimumamount of hydrated inorganic flame retardant. The oxygen index is at thelower end of what is acceptable and the viscosity is on the higher end,although this product is still within an acceptable range to the presentinvention.

Example 7 illustrates the maximum amount of resin desirable and thesmoke number is greater than what would be preferred in the presentinvention.

Example 8 illustrates the maximum amount of the zinc borate flameretardant which is desirable. The oxygen index is slightly below thatwhich is preferred in the present invention, although it is acceptable.

Comparative Example A illustrates a composition having a resin contentwhich is too high resulting in a high smoke number, 8, indicating thatthe smoke generation is unacceptable for the present invention.

We claim:
 1. A High Efficiency Particulate Air Filter comprising:a) a material effective for filtering airborne contaminants; and b) a hot melt adhesive applied to said material said adhesive comprising:i) about 10% to about 60% by weight of the adhesive of at least one copolymer of ethylene; ii) about 10% to about 50% by weight of the adhesive of a hydrated inorganic flame retarding compound; and iii) about 5% to about 30% by weight of at least one high melting point wax; and 0% to about 10% by weight of at least one tackifying resinwherein said filter is pleated after application of said adhesive to said material.
 2. The filter of claim 1 wherein said hot melt adhesive is applied in a pattern selected from the group consisting of continuous and stitched.
 3. The filter of claim 1 wherein said filter material is made of a fiber glass composite material.
 4. The filter of claim 1 wherein said hydrated inorganic compound is selected from the group consisting of alumina trihydrate, magnesium hydroxide and mixtures thereof.
 5. The filter of claim 1 wherein said hot melt adhesive further comprises up to about 40% by weight of the composition of zinc borate.
 6. The filter of claim 1 wherein said hot melt adhesive has an oxygen index of greater than about
 23. 7. The filter of claim 1 wherein said hot melt adhesive has an oxygen index of greater than about
 25. 8. The filter of claim 1 wherein said hot melt adhesive has a smoke number of less than about
 5. 9. The filter of claim 1 wherein said hot melt adhesive has a yellow-blue index from about 0 to about 5 and a black-white index from about 75 to about
 100. 10. The filter of claim 1 formed by a method comprising the steps of:a) applying said adhesive to said filtering material said filtering material being in a continuous strip and in an unpleated state; and b) pleating the filter material by folding it back and forth until it is in an accordion-like shape while said hot melt adhesive remains ductile.
 11. A High Efficiency Particulate Air Filter comprising:a) a material effective for filtering airborne contaminants; and b) a hot melt adhesive applied to said material said adhesive consisting essentially of:i) about 10% to about 60% by weight of the adhesive of at least one copolymer of ethylene; ii) about 10% to about 50% by weight of the adhesive of a hydrated inorganic flame retarding compound; and iii) about 5% to about 30% by weight of at least one high melting point wax; and iv) 0% to about 10% by weight of at least one tackifying resinwherein said filter is pleated after application of said adhesive to said material. 